1. Field of the Invention
The present invention relates to prediction techniques relating to the life span of a manufacturing apparatus which uses a rotary machine. In particular, the invention relates to a system for predicting the life of the rotary machine, a method for predicting the life of the manufacturing apparatus which uses the rotary machine and a manufacturing apparatus including the rotary machine.
2. Description of the Related Art
Failure diagnosis has become important to ensure efficient semiconductor device manufacturing. In recent years, especially as the trend towards small volume production of many different items of system LSI increases, an efficient yet highly adaptable semiconductor device manufacturing method has become necessary. It is possible to use a plurality of small-scale production lines adapted for miscellaneous purposes in view of the efficient production of different semiconductor devices. However, if many small-scale production lines are constructed by merely miniaturizing large-scale production lines, investment efficiency may be reduced due to a decrease in the rate of manufacturing apparatus utilization. To rectify this situation, there is a method whereby different manufacturing processes are performed by one piece of manufacturing equipment. For example, in a LPCVD apparatus using a dry pump for the evacuation system, reactive gases and reaction products differ and formation situations for the reaction products within the dry pump differ depending on the type of manufacturing processes. Therefore, the manufacturing process affects the life of the dry pump.
If the dry pump should have a failure during a specific manufacturing process, then the lot products being processed will be defective. Moreover, excessive maintenance of the manufacturing apparatus may become necessary due to microscopic dust caused by residual reactive gases within the manufacturing apparatus. Implementation of such excessive maintenance causes the manufacturing efficiency of the semiconductor device to drop dramatically. If regular maintenance is scheduled with a margin of safety in order to prevent such sudden failures during the manufacturing process, the frequency of maintenance work on the dry pump may become astronomical. Not only does this increase maintenance costs, but also the decrease in availability of the semiconductor manufacturing apparatus is conspicuous due to changing the dry pump, which causes the manufacturing efficiency of the semiconductor device to decline sharply. In order to use a common semiconductor manufacturing apparatus for a plurality of processes, as is necessary for an efficient small-scale production line, it is desirable to accurately diagnose vacuum pump life and to operate the dry pump without having any wasted time.
Previously, some methods of diagnosing dry pump life have been proposed. Basically, a state of the dry pump may be monitored by characteristics such as the motor current, vibration, and temperature, and methods have been provided to predict the pump life from variations in these characteristics (refer to Japanese Patent Application P2000-259222). In particular, dry pump life span diagnosis methods have mainly been provided by monitoring the state of the dry pump through vibrations caused by the rotation of a rotor. Since a diagnosis using the vibration can be accomplished through measurements taken by merely attaching an accelerometer to a side of the dry pump, it has gained attention as a simple and easy method for predicting pump life span. In addition, a method for predicting life span has been proposed whereby acoustic emission signals as vibration data are analyzed using an analog-to-digital (A/D) conversion (refer to Japanese Patent Application H11-62846).
Residue of reaction products accumulated inside the dry pump may be determined by a variation of a frequency of integral multiples of a normal vibration frequency to be characteristics for the dry pump instead of the normal vibration frequency of the dry pump. In a method for predicting life of the rotary machine according to an earlier example, as shown in FIG. 1, a signal from a vibration gauge 117 measuring a vibration of a dry pump 113 is amplified in an amplifier 181 and converted into a digital signal in an analog-digital (A/D) converter 118. Then, only a particular frequency component is taken out after Fourier transform in data processing unit 119.
In the method for taking out a particular frequency component by the Fourier transform from the digital signal converted by the A/D converter, there is problems that a quantity of data to process is enormous and a vibration variation with an extremely short time of less than or equal to one second cannot be evaluated. In addition, the measurement system becomes large in scale, and high in cost. Furthermore, a phenomenon occurs in which a peak frequency of the vibration fluctuates when reaction products have accumulated in the dry pump. Therefore, it is necessary to provide a method to evaluate peak acceleration precisely, even when the peak frequency fluctuates.
As mentioned above, in the method for predicting a life of a dry pump using a vibration according to the earlier example, there is a problem in the cost of the measurement system, the quantity of data, an interval between the measurement time and stability of the process. It is desired to provide a life prediction method having a simple and easy procedure which is highly stable and accurate, in an inexpensive measurement system.